Fin Whale Sound Reception Mechanisms: Skull Vibration Enables Low-frequency Hearing

Professor Petr Krysl

Hearing mechanisms in baleen whales (Mysticeti) are essentially unknown but their vocalizations overlap with anthropogenic sound sources. Synthetic audiograms were generated for a n whale by applying nite element modeling tools to X-ray computed tomography (CT) scans. We CT scanned the head of a small n whale (Balaenoptera physalus) in a scanner designed for solid-fuel rocket motors. Our computer ( nite element) modeling toolkit allowed us to visualize what occurs when sounds interact with the anatomic geometry of the whale’s head.

Our publication in PLOS One of 2015 was the rst account of the computational construction of an audiogram of an experimentally

unapproachable marine mammal. Simulations reveal two mechanisms that excite each bony ear complex, (1) the skull-vibration enabled bone conduction mechanism and (2) a pressure mechanism transmitted through soft tissues. Bone conduction is the predominant mechanism. The mass density of the both bony ear complexes and their rigid attachments to the skull are universal across the Mysticeti, suggesting that sound reception mechanisms are similar in all baleen whales. Interactions between incident sound waves and the skull cause deformations that induce motion in each bony ear complex, resulting in best hearing sensitivity for low-frequency sounds. This predominant low-frequency sensitivity has signi cant implications

for assessing mysticete exposure levels to anthropogenic sounds. The din of man-made ocean noise has risen steadily over the last half century. Our results provide valuable data for U.S. regulatory agencies and concerned large-scale industrial users of the ocean environment. This study transforms our understanding of baleen whale hearing and provides a means to predict auditory sensitivity across a broad spectrum of sound frequencies.

The publication was in the rst year since its appearance viewed 6 1⁄2 thousand times and downloaded almost 900 times. This is a good indication of the timeliness and relevance of the investigation.

Fin Whale Sound Reception Mechanisms: Skull Vibration Enables Low-frequency Hearing

In collaboration with Ted W. Cranford, San Diego State University, Department of Biology, and Quantitative Morphology Consulting, Inc., 2674 Russmar Dr., San Diego, CA 92123-3422. We thank the following people for their support on various aspects of this project. Michael Wiese, James Eckman, and Dana Belden at the O ce of Naval Research (N00014-12-1-0516); Frank Stone, Ernie Young, and Robert Gisiner at the Chief of Naval Operations (CNO45) along with Curtis Collins and John Joseph at the Naval Postgraduate School (N00244-08-1-0025).